Thrift IDL : service response as list

In thrift IDL, can the service response be list or map also?

Because, normally I have seen it to be some struct or some primitive types like string, double, etc.

Also, what is the source from where I can verify? Please also mention the source.

Solution

Sure it can:

service FooBar {
    list<double>  Foobarizer()
}

is perfectly legal.

So why are people using structs then? Well, it makes the API extensible. And this has to do with what is called "soft versioning".

Here's an Example:

Consider you want to add another flag that gives some valuable additional information. How can we add it to the response? With only a list, you are lost, because changing it to something like

struct FoobarizerReturn {
  1: list<double>  data
  2: bool theValuableInfo     // added in V2
}

service FooBar {
    //list<double>  Foobarizer()
    FoobarizerReturn  Foobarizer()
}

will essentially break the API for older clients. To keep it compatible, you would have to change your IDL instead like so:

service FooBar {
    /** V1 deprecated */
    list<double>  Foobarizer()  
    /** V2 use this now */
    FoobarizerReturn  FoobarizerV2()
}

which has at least three disadvantages:

it requires additional code at the server end
it causes additional work at the client's end
is just butt-ugly (that's a technical term)

Hence, the most forward compatible solution is to start with a struct from the beginning, which can later easily be extended as needed w/o breaking compatibility.

struct FoobarizerReturn {
  1: list<double>  data
   // more data to come later
}

service FooBar {
    FoobarizerReturn  Foobarizer()
}